It is well established that certain critical portions of the fuel-air mixing process can be influenced by the thermal environment wherein fuel and air first come into contact with each other, i.e., the intake port. While the air that passes through the intake port is only slightly influenced by the temperature of the intake port walls, any liquid fuel that exists as a film on the intake port wall will be significantly affected by the temperature. Thus, the liquid-vapor equilibrium and the mixing process will be affected by this.
The temperature of the intake port walls can influence the heat flux from the walls to any liquid fuel films. Conventional design practice places the intake port in direct contact with engine coolant, and therefore the temperature is governed principally by that of the coolant with a slow warm up period and a near constant temperature thereafter throughout the engine operating regime.
Further, conventionally designed intake ports are manufactured with a port-core casting technique which utilizes relatively large wall thicknesses surrounded by engine coolant, resulting in a high degree of thermal inertia. Also undesirable are locational and dimensional variability and relatively “rough” surface finish associated with the port-core casting technique.
Disadvantageously, the slow warm up and constant temperature of conventional intake ports is not ideal with respect to emissions, fuel efficiency, and performance. Thus, there exists a need to thermally decouple the temperature of the intake port walls from the engine cooling system to align the temperature closer to idealized thermal conditions for intake ports. Further, there exists a need for a manufacturing process for the thermally-decoupled intake port which adds an air gap between the intake port walls and the cylinder head surface while providing a more uniform and polished surface from the port-casting technique used in conventional intake ports.
U.S. Pat. No. 5,099,808 to Matsuura et al. discloses a cylinder head assembly with intake ports having a thermally insulated barrier made of a ceramic material covering the intake port wall for purposes of reducing air flow resistance by reducing heat transfer between the cylinder head and the inducted air. However, the Matsuura et al. reference fails to disclose thermally decoupling the surface temperature of the intake port wall from the coolant in order to match ideal thermal characteristics of an intake port. Further, the Matsuura et al. reference fails to disclose a hydroform manufacturing process to form a low-thermal-inertia intake port.